I think it is interesting to watch the debate about dairy taking place in the larger 'paleo diet' community. When I go searching on the Web for information about 'dairy' it can be difficult to find anything useful, but when I search specifically for 'paleo dairy' then at least the debate starts to come into focus.
If you buy dairy products from a store that sells "factory food," you are going to be consuming something awful. It doesn't matter if you have genes (from both parents) that are "adapted" to dairy or not. Nobody is adapted to industrial "dairy."
If you manage to find dairy products made from raw milk from "heritage," grain-free, fully-pastured cows that have been well treated, then you can start to ask about whether milk (not "milk") is a suitable human food. Any genetic adaptation to milk that occurred over the last 10,000 years would be to that kind of milk, not the the kind of "dairy" you find in stores today.
I don't drink milk. If I went to enough trouble, however, I think there is a small chance I might be able to find healthy raw milk near where I live. I'm not sure. I don't think it is illegal to sell it here, but I am not sure that I could find raw milk from grain-free pastured cows that were properly treated. Finding milk from heritage breeds (as opposed to modern breeds) would be even more difficult. Finding other products made from such milk is, for me, not very possible. So I would have to make them myself, and I consider that more trouble than it is worth since neither the benefits nor the risks are clear.
If you do have access to natural, pre-industrial dairy and you have the genes to digest both lactose and casein correctly (special testing might be needed) and you are not allergic to milk then you might want to dig deeper. But then you are going to find that generally in nature, animals don't drink the milk of other animals or continue drinking it past infancy. And while some people have genes that let them do it anyway, being able to digest it is not the same as being fully adapted to it. This is way to much for me to spend time on, since I don't have access that kind of dairy anyway.
In order to include a variety of fat sources in my diet I do consume a limited amount of "organic cultured butter" from "pasture-based" cows (yes, they can sometimes be grain-fed, depending on the season, but it is organic grain -- whoopee). It's not local. The producer makes another, better grade, but it is not sold here. I take my chances with it, and don't eat a lot. You can't really buy traditional fermented (from raw) butter, at least not here. I think that would be the best choice, if you can make it.
I also consume a significant amount of a locally-produced high-grade organic ghee (which costs $20 for a medium-sized jar). There are similar issues with what "organic" really means, but the risk is lower than with butter. I would not recommend less expensive products.
For more information, Google 'paleo dairy' and see what you come up with! But look beyond just that which matches with your beliefs and preferences.
